Walkthrough captions follow the voice word by word

When Obeya answers with a narrated walkthrough, its caption now marks the word being spoken, with the words already said in full colour and the ones still to come faded. The timing comes from hearing each voiced sentence back with the speech recognition of voice input, so the mark follows what the voice really says, pauses included. On flow slides, the boxes build up one by one as the narration reaches them.